1. Field of the Invention
The invention concerns a laminated glass pane with a transparent functional film embedded between laminating layers, which incorporates a recess, where in the area of the recess of the functional film is arranged a transparent auxiliary film, whose thickness corresponds essentially to the thickness of the functional film. The invention concerns in particular laminated safety glass pane of the aforementioned construction.
Recess in the functional film means within the scope of the invention an opening completely bounded by the gfunctional film within the surface of the functional film, as well as open cutouts in the edge area of the functional film extending towards the edge. The invention includes in particular such laminated glass panes where the edge of the functional film is, at least in some areas, set back from the edge of the laminated glass pane, where the film-free edge area so formed forms the said recess.
Laminated glass panes consist of at least one rigid pane of inorganic or organic glass which, in the case of laminated safety glass panes is bonded to plastic layers imparting safety properties, and is generally bonded to at least one other glass pane. Between the various layers of the laminated glass panes are arranged laminating layers whose function is to join the layers adhesively to one another. The laminating layers impart the required safety properties, either through suitable material selection and thickness themselves, or establish the bond with separate layers of the laminate imparting the safety properties. In practice, films of polyvinylbutyral or ethylene/vinyl acetate copolymers are used for the laminating layers, their thickness being typically 0.38 mm or a multiple thereof.
2. Description of the Prior Art
Laminated glass panes of the aforementioned construction, in particular for vehicle applications, are increasingly being provided with additional functional films embedded between laminating layers, with the aid of which the laminated glass panes are intended to assume additional functions, such as for example solar control properties or heatability. Known functional films consist of thermoplastic substrate films, for example of biaxially stretched polyethylene terephthalate (PET) or similar materials, with a thickness of approximately 10-100 .mu.m, which are coated with a thin-layer system (U.S. Pat. No. 4,799,745).
Normally, the functional films possess the same external dimensions as the other layers of the laminated glass pane and thus end at its edge. It is already known practice however to use functional films with a recess in the edge area for a variety of applications.
If one uses functional films with a recess as interlayer in laminated glass panes, this leads to thickness "stepping" occurring in the transition area from the recess to the functional foil--referred to below as edge of the recess--which, according to the thickness of the functional film, causes more of less disturbing optical distortion (lens effect).
U.S. Pat. No. 5,208,080 discloses a laminated glass pane of the generic construction, where the functional film possesses smaller dimensions than the individual glass panes, that is to say is provided with a surrounding recess in the edge area. In the area of the surrounding recess are arranged bordering on the edge of the recess auxiliary strips of thermoplastic material, preferably of the material of the laminating layers, abutting the functional film. In this way, it is intended to embed the functional film entirely in laminating layers. It has been found that, when employing this method, it is not possible to reliably prevent the inclusion of air bubbles between the edge of the recess and the auxiliary strips. In addition, disturbing optical distortion can occur in the area of the edge of the recess.